The unexpected death of a young girl with a big smile and "wonderful attitude" to life has shocked her Masterton primary school.

Eve Bennett, 13, died in her sleep this week at her Masterton home.

She was found by her mother, Wendy, on Thursday morning.

It is believed her unexpected death, the cause of which was yet to be determined, was linked to a medical condition Eve suffered.

Lakeview School principal Ed Hodgkinson said staff and pupils had been left shocked by the news.

"It was a very, very sad day for us," he said. "We had to tell her teacher, who was obviously very sad, as well as the teacher aide who was working with her."

Staff and pupils had held a minute's silence for Eve and were offered emotional support on Thursday and again yesterday.

The school had also set up a tribute table, which people had contributed to with letters, flowers and photos.

The table was to be taken to the Masterton Town Hall last night so Eve would still "be part" of a large Pasifika celebration the school was involved in.

Mr Hodgkinson said Eve had been a pupil at the school since she was 5, and would be "missed greatly".

"Eve was a wonderful young girl with a wonderful smile, and she went before her time.

"She had challenges brought on by medical conditions, that made academic aspects a challenge for her, but what she did have in abundance was a wonderful attitude."

Online tributes flooded in yesterday to a "kind-hearted girl that wouldn't hurt anyone".

"You have touched so many lives and it has been awesome seeing you grow up, we will always love you and you will be forever in our hearts," read a Facebook post.

Along with her mother, Eve leaves behind her father, Gordon, and two older brothers, Hayden and William.

Senior Sergeant Carolyn Watson, of Wairarapa, said an autopsy was being carried out yesterday to determine the cause of death. It was believed to be linked to her medical condition and police were not investigating further.

A funeral service for Eve will be held at Masterton's Lighthouse Church at 2pm on Wednesday.